Evaluation of iron-based oxygen carrier supported on alumina/titania for charcoal combustion through chemical looping process

Abstract

Hematite supported on alumina or alumina/titania was fabricated to serve as an oxygen carrier in the chemical looping combustion (CLC) of charcoal. The reduction rate of Fe2O3/Al2O3 and Fe2O3/Al2O3/TiO2 particles increased with the reactor inlet’s CO concentration and displayed a slight effect from elevated operating temperatures. Applying the shrinking core model, the mass transfer coefficients (kg) for the reduction of Fe2O3/Al2O3 and Fe2O3/Al2O3/TiO2 by CO were found to be 0.16 and 0.22 mm s–1, respectively, and using the Fe2O3/Al2O3 and Fe2O3/Al2O3/TiO2 to combust charcoal resulted in carbon conversion rates of approximately 61.8% and 47.2%, respectively, when the inlet steam flow rate was set to 221.4 mmol min–1. Significantly, a higher inlet steam flow rate may not be advantageous when employing iron-based oxygen carriers. More heat was released during combustion with the Fe2O3/Al2O3 than with the Fe2O3/Al2O3/TiO2 due to a high flow rate for the former being used. When Fe2O3/Al2O3/TiO2 was used as the oxygen carrier, the particles, which contained a large percentage of Fe2O3, exhibited high reactivity to syngas (CO/H2); thus, less Fe2O3/Al2O3/TiO2 than Fe2O3/Al2O3 was required to combust the charcoal.